1. Field of the Invention
The present invention relates to a method and apparatus for detecting or inspecting the appearance and shape of a workpiece such as a tire or tire part by imaging it.
2. Description of the Prior Art
In the prior art, as one of product inspection methods, a product is imaged by a line camera to judge whether the surface state such as discoloration or stains of the workpiece is acceptable or not from the obtained appearance data. However, discoloration or stains can be judged accurately from data on the appearance imaged by the line camera but the shape of the workpiece cannot be judged accurately. Therefore, a light-section method in which the surface of the workpiece is imaged by an area camera by applying slit light to detect the shape of the workpiece from the obtained image data is employed.
To inspect the shape of a tire by the above light-section method, as disclosed by JP-A 11-138654 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), for example, slit light is applied to the surface of the tire by floodlight means such as a semiconductor laser to image a portion illuminated by the above slit light with an area camera, the obtained image data is converted into secondary coordinate values to obtain the outer shape of the tire, and the shape is compared with the pre-stored image of the workpiece to inspect the shape of the tire such as a beat, tread or side wall portion. At this point, the shape and circularity of the tire in a predetermined region can be detected and inspected by turning the floodlight means, the imaging means and the tire relative to one another.
However, in the above light-section method, the circularity, surface unevenness or scratch can be checked but not discoloration and stains. Then, there is proposed an apparatus for imaging the same line portion of a workpiece with a line camera and an area camera at the same time (JP-A 2001-249012). As shown in FIG. 5, this is aimed to inspect the appearance and shape of a tire T mounted on a rotary table 58 turned by a motor 57 at the same time by using imaging means 50 which comprises a floodlight (illuminator) 51 making use of a white LED, line camera 52, line reflection mirror 53, laser floodlight 54 having a wavelength of 680 nm and area camera 55, all built in one holding frame 56, to pick up a slit image of the tire T illuminated by light from the above floodlight 51 with the line camera 52 so as to obtain monochromatic or color appearance data and to input shape data on a ridge line on the surface of the tire T obtained by imaging a portion illuminated by slit light from the laser floodlight 54 with the area camera 55. The above obtained appearance data and shape data are transmitted to the appearance image forming means 61 and shape image forming means 62 of an appearance and shape judging unit 60 to be processed, compared with tire appearance and shape data pre-stored in tire information storage means 65 to judge whether the appearance and shape are acceptable or not, and finally whether the tire is acceptable or not is judged by overall judging means 66.
However, in the above method, the apparatus becomes bulky and it is difficult to optically align a line portion to be imaged by the line camera 52 with a line portion to be imaged by the area camera 55. Although it is possible to align the obtained two images by software, data processing becomes complicated and storage means or computing means for processing data is necessary.
It is an object of the present invention which has been made in view of the above problems of the prior art to provide a method and apparatus for detecting the appearance and shape of a workpiece by imaging the workpiece to detect the coordinates and brightness of the workpiece with a simple structure and a method and apparatus for inspecting the appearance and shape of a workpiece using this detection method.